Many different types of hard disk drives are available. Characteristics that differentiate one hard disk drive from another include the storage capacity of the drive, the access time to read or write data, the number of input and output operations per second (IOPS), and other characteristics. Users and system designers generally select the appropriate hard disk drive for a given application and use case. The selection of the hard disk drive is based on any of the aforementioned performance characteristics, price, etc.
Once a particular hard disk drive is purchased and installed into a system, the drive provides its rated storage size and performance. If it turns out the user later needs a hard disk with a different amount of storage or other performance characteristic, the user can purchase another hard disk drive. Such decisions, however, are costly in terms of the cost of the replacement drive and the maintenance to power off the old drive, disconnect the old drive, install the new drive, connect the new drive to the system, etc.